It has been generally accepted that the primary event in gene expression is asymmetric in the sense that only one of the two DNA strands in the gene serves as a template for RNA. However, during the last years, we have shown that in the mitochondrial genetic system in HeLa cells and in the DNA tumor viruses SV40 and polyoma, the concept of asymmetric transcription is wrong and the alternative possibility, that of symmetrical transcription is taking place. Similar mode of transcription has been shown to occur also with Adeno and Herpes viruses. Symmetrical transcription predicts regulation of gene expression at the post-transcriptional level and it involves the selective degradation of particular RNA sequences. Using three systems which include: 1) SV40 infected whole cells, 2) isolated nuclei and 3) a cell free system, I propose to study the detailed mechanism of transcription of SV40 and polyoma DNA and the control mechanisms which operate at the post-transcriptional level. During these studies we shall also try to answer the following: 1) What is the role of methylation in RNA processing? 2) Identification and characterization of cellular sequences in high Molecular Weight Viral RNA as an approach to determine integration sites of the viral DNA in the chromosomal DNA. 3) The effect of interferon on SV40 transcription. 4) What is the sub-cellular fraction where the processing of the viral RNA takes place? and 5) Mapping of the T-Ag binding sites on SV40 DNA molecule, and the effect of T-Ag on early and late transcription.